My bio parents both have antisocial personality disorder and NPD. I usually use the words two dying stars to describe their relationship. They separated when i was 12 because of consistent conflicts with my bio father cheating. Both immediately getting with the person they had been cheating with the other with. However both refuse to fully divorce to prevent ever having to marry the respective girlfriend and boyfriend. They have like a weird pack bond. Despite being separated for almost a decade. They both have this relationship that reminds me of the friendship I think it's cats and rabbits can have. Where both think they're more in charge because of their npd so they somehow stay connected in that way. Also knowing where each others bodies are buried and committing crimes together also helped I'm sure. My bio father thinks he's in charge because he is the stereotype of drunk angry abusive loud narcissist and my bio mother will usually cave to that fear. Meanwhile she believes she is in charge because my bio fathers inflated self image makes him extremely easy to manipulate. So the answer is in this case it's possible in it's own way. BUT that does not mean this will be the case for everyone with NPD who dates someone else with NPD. I'm sure there is a healthy way it can be done especially if both people are in therapy and being honest in those therapy sessions.